Modern Physics- General Introduction - Thermodynamics And Electromagnetism

Modern Physics- General Introduction - Thermodynamics and Electromagnetism

Slide 1

Welcome to the lecture on Modern Physics.
Today, we will cover the topics of Thermodynamics and Electromagnetism.
These topics are crucial for understanding various phenomena in the world around us.
Let’s dive in and explore the fascinating world of Modern Physics!

Thermodynamics

Thermodynamics deals with the study of energy, heat, and the relationship between them.
It helps us understand how energy can be converted from one form to another.
The laws of thermodynamics have wide applications, from studying heat engines to understanding the behavior of gases.
Thermodynamics provides a foundation for understanding many practical areas such as power generation, refrigeration, and climate science.

Laws of Thermodynamics

First Law of Thermodynamics: Energy can neither be created nor destroyed but can only change from one form to another.

Second Law of Thermodynamics: In any energy conversion process, the overall entropy of a closed system always increases.

Third Law of Thermodynamics: It is impossible to reach absolute zero (zero Kelvin) through a finite number of processes.

Applications of Thermodynamics

Heat engines: Understanding the efficiency and working of engines such as the Otto cycle and steam engines.
Refrigeration and air conditioning: Understanding the principles behind cooling systems and heat pumps.
Power generation: Studying the behavior of turbines in power plants.
Solar energy: Exploring the conversion of solar radiation into usable energy.

Electromagnetism

Electromagnetism is the branch of physics that deals with the relationship between electricity and magnetism.
It studies the behavior of electric charges, electromagnetic waves, and the interaction between charges and magnetic fields.
Electromagnetism plays a vital role in various technological applications such as generators, motors, transformers, and telecommunications.
Understanding electromagnetism is essential for comprehending the functioning of everyday devices like mobile phones and electric circuits.

Electromagnetic Fields

An electric field is created by stationary charges and affects other charges in its vicinity.
A magnetic field is produced by moving charges or currents and interacts with other moving charges or currents.
Both electric and magnetic fields are interrelated and collectively called an electromagnetic field.
Maxwell’s equations describe the behavior of electromagnetic fields.

Electric Circuits

Electric circuits are an integral part of our daily lives.
They consist of various components like resistors, capacitors, and inductors connected through conducting wires.
Kirchhoff’s laws are used to analyze and solve electric circuits.
Examples of circuits include series circuits, parallel circuits, and combinations of both.

Magnetic Fields and Forces

A magnetic field exerts a force on a moving charged particle or a current-carrying wire.
The force is given by the equation F = qVB, where F is the force, q is the charge, V is the velocity, and B is the magnetic field.
Understanding the behavior of magnetic fields and forces is crucial for applications such as motors, transformers, and magnetic resonance imaging (MRI).

Electromagnetic Waves

Electromagnetic waves are transverse waves consisting of electric and magnetic fields oscillating perpendicular to each other.
They can propagate through vacuum as well as various media.
Electromagnetic waves span a wide range of frequencies, from radio waves to gamma rays.
The speed of electromagnetic waves in vacuum is approximately 3 × 10^8 meters per second, denoted by the symbol c.

Relation between Electricity and Magnetism

One of the fundamental relationships in electromagnetism is known as Ampere-Maxwell’s law.
It states that a changing magnetic field creates an electric field, and a changing electric field creates a magnetic field.
This interdependence of electric and magnetic fields forms the basis of electromagnetic induction, one of the key principles behind the working of generators and transformers.

Thermodynamic Processes

Thermodynamic processes are classified into different types:
- Isothermal process: Temperature remains constant while other parameters (pressure, volume) change.
- Adiabatic process: No heat exchange occurs between the system and its surroundings.
- Isobaric process: Pressure remains constant while other parameters change.
- Isochoric process: Volume remains constant while other parameters change.
- Reversible process: Occurs slowly and follows well-defined steps.
- Irreversible process: Occurs rapidly and does not follow well-defined steps.

Heat and Work in Thermodynamics

In thermodynamics, heat (Q) is the transfer of energy due to a temperature difference.
Work (W) is the transfer of energy due to a force acting over a distance.
The first law of thermodynamics can be expressed as:
- Q = ΔU + W
- ΔU = Change in internal energy of the system

Entropy and the Second Law of Thermodynamics

Entropy (S) is a measure of the randomness or disorder in a system.
The second law of thermodynamics states that the entropy of an isolated system always increases or remains constant in a spontaneous process.
The change in entropy (ΔS) is given by:
- ΔS = Q_rev / T
- Q_rev = Reversible heat transfer
- T = Temperature in Kelvin

Carnot Cycle

The Carnot cycle is an idealized thermodynamic cycle that consists of four reversible processes.
It is used to model the behavior of ideal heat engines.
The efficiency of a Carnot cycle is given by:
- Efficiency = 1 - (T_cold / T_hot)
- T_cold = Absolute temperature of the cold reservoir
- T_hot = Absolute temperature of the hot reservoir

Laws of Electromagnetism

Gauss’s Law: The total electric flux through any closed surface is proportional to the total electric charge enclosed by the surface.
Faraday’s Law: The induced electromotive force (EMF) in a closed loop is equal to the rate of change of magnetic flux through the loop.
Ampere’s Law: The magnetic field created by an electric current is proportional to the current and inversely proportional to the distance from the current.

Electric Potential and Potential Difference

Electric potential (V) is the amount of work needed to move a unit positive charge from a reference point to a specific location in an electric field.
Potential difference (V) is the difference in electric potential between two points.
It is measured in volts (V) and is related to electric field strength (E) by the equation:
- V = Ed
- E = Electric field strength
- d = Distance between the points

Capacitors

A capacitor is a device that stores electrical energy in an electric field.
It consists of two conducting plates separated by a dielectric material.
The capacitance (C) of a capacitor is a measure of its ability to store charge and is given by:
- C = Q/V
- Q = Charge stored in the capacitor
- V = Potential difference across the capacitor

Magnetic Induction

Magnetic induction, also known as magnetic flux, is a measure of the strength of a magnetic field passing through a surface.
It is denoted by the symbol Φ.
The magnetic induction (B) is defined as the magnetic flux per unit area perpendicular to the field lines:
- B = Φ / A
- B = Magnetic induction
- Φ = Magnetic flux
- A = Area

Electromagnetic Spectrum

The electromagnetic spectrum encompasses all the different types of electromagnetic waves.
It is divided into several regions based on the wavelength or frequency of the waves.
Examples of regions in the electromagnetic spectrum include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Applications of Electromagnetism

Electric generators: Converts mechanical energy into electrical energy by electromagnetic induction.
Transformers: Used to step up or step down voltage in power transmission systems.
Electric motors: Work based on the interaction between magnetic fields and electric currents to produce mechanical motion.
Electromagnetic waves: Used in technologies such as wireless communication, radar, and medical imaging (CT scans, MRI).

Thermodynamics Equations

The ideal gas law equation: PV = nRT
The specific heat capacity equation: Q = mcΔT
The efficiency of a heat engine equation: Efficiency = 1 - (Tc/Th)
The relationship between work and heat in an isothermal process: W = -Q
The relationship between work and heat in an adiabatic process: W = -ΔU

Carnot Engine Example

A Carnot engine operates between a hot reservoir at 500 K and a cold reservoir at 300 K.
The heat absorbed from the hot reservoir is 5000 J.
Calculate the work done by the engine and its efficiency.
Using the equation for efficiency:
- Efficiency = 1 - (Tc/Th)
- Efficiency = 1 - (300/500)
- Efficiency = 1 - 0.6
- Efficiency = 0.4 or 40%
The work done by the engine can be calculated using the equation:
- Efficiency = W/Q
- W = Efficiency x Q
- W = 0.4 x 5000 J
- W = 2000 J

Electric Field and Potential Examples

A point charge q = 2 μC is placed at a distance r = 3 meters from another point charge Q = -4 μC.
Find the electric potential at a point on the line connecting the two charges.
Using the equation for electric potential:
- V = kQ/r
- V = (9 × 10^9 N·m^2/C^2) × (-4 × 10^-6 C) / 3 m
- V ≈ -12 × 10^3 V

Capacitor Example

A capacitor has a capacitance of 10 μF and is connected to a 12 V battery.
Calculate the charge stored in the capacitor.
Using the equation for capacitance:
- C = Q/V
- Q = C x V
- Q = (10 × 10^-6 F) × 12 V
- Q = 120 μC

Magnetic Field and Flux Example

A wire loop with an area of 0.2 m² is placed in a magnetic field of 0.5 T.
Calculate the magnetic flux through the loop.
Using the equation for magnetic flux:
- Φ = B x A
- Φ = (0.5 T) × (0.2 m²)
- Φ = 0.1 Wb (weber)

Electromagnetic Waves Example

An electromagnetic wave travels at a frequency of 2 GHz (2 × 10^9 Hz).
Calculate the wavelength of the wave.
Using the equation for wave speed:
- Speed of light = Frequency x Wavelength
- Wavelength = Speed of light / Frequency
- Wavelength = (3 × 10^8 m/s) / (2 × 10^9 Hz)
- Wavelength = 0.15 m or 15 cm

Gauss’s Law Example

A closed surface encloses a point charge of +5 μC.
Calculate the electric flux through the surface if it has an area of 4π m².
Using Gauss’s law:
- Electric flux = (Charge enclosed) / (Permittivity of free space)
- Electric flux = (5 × 10^-6 C) / (4π × 8.85 x 10^-12 C²/N·m²)
- Electric flux = 1.79 x 10^6 N·m²/C

Faraday’s Law Example

A magnetic field pointing into the page is decreasing at a rate of 0.5 T/s.
Calculate the induced electromotive force (EMF) in a wire loop of area 0.1 m².
Using Faraday’s law:
- EMF = - (Rate of change of magnetic flux)
- EMF = - (Change in magnetic flux / Change in time)
- EMF = - (0.5 T/s) × (0.1 m²)
- EMF = -0.05 V

Ampere’s Law Example

A straight wire carries a current of 3 A.
Calculate the magnetic field at a distance of 0.1 m from the wire.
Using Ampere’s law:
- Magnetic field = (Permeability of free space) × (Current) / (2π × Distance)
- Magnetic field = (4π × 10^-7 T·m/A) × (3 A) / (2π × 0.1 m)
- Magnetic field = 6 × 10^-6 T or 6 μT

Applications of Electromagnetism in Daily Life

MRI scanners use magnetic fields and radio waves to create detailed images of the body.
Electric generators convert mechanical energy into electrical energy using electromagnetic induction.
Transformers step up or step down voltage in power transmission systems.
Electric motors convert electrical energy into mechanical energy by the interaction of magnetic fields and electric currents.
Wireless communication systems use electromagnetic waves for transmitting and receiving signals.